[Action Knot] Form submission redirection strategy

### Current
Action Knot calls Adapter with submitted form data. Adapter process form data and returns JSON model with signal `success`. In form definition we have information that we expect to stay on the same page for success signal (`_self` value). Action Knot does not set new location header and set "next" transition for Knots Routing. It means that user is not redirected. This leads to problems with page refreshing.

### Proposal
We should be redirected user to current page for `success` signal. We need to design system should behave for form validation errors. How should we pass information from invoked Adapter to next GET request (redirect).

Start by tracing Action Knot's call to Adapter, the form definition's `_self` success setting, and the `next` transition in Knots Routing through the subsequent GET. Define the behavior for successful submissions, validation errors, and passing information across the redirect; done means the strategy is agreed and documented.

Written by the indexing model from the issue text.